Q. Why does a needle sink in water while an iron ship floats on it ?
A. According to the law of floatation, a body floats in a liquid when the weight of the whole body is equal to the weight of the liquid displaced by the immersed portion of the body. A needle or solid steel ball sinks in water because the weight of water displaced by it is less than the weight of needle or steel ball. An iron ship is so shaped that it can displace a large volume of water. The weight of the water displaced by the immersed portion of the ship is equal to the weight of the ship. Hence, it can float.